Students investigate the rate of photosynthesis in pondweed (Elodea) by measuring the volume of oxygen gas produced at different distances from a light source. They use a capillary tube connected to a syringe to collect the gas bubble released by the plant.
Table of Results:
Distance of light source (cm)Volume of oxygen gas collected in 15 minutes (mm3)1045202830184012508 \begin{array}{|c|c|} \hline \text{Distance of light source (cm)} & \text{Volume of oxygen gas collected in 15 minutes (mm}^3\text{)} \\ \hline 10 & 45 \\ \hline 20 & 28 \\ \hline 30 & 18 \\ \hline 40 & 12 \\ \hline 50 & 8 \\ \hline \end{array} Distance of light source (cm)1020304050Volume of oxygen gas collected in 15 minutes (mm3)452818128Identify the independent variable and the dependent variable in this investigation.
Explain why using a capillary tube and syringe to measure the rate of photosynthesis is more accurate than counting the number of bubbles of gas released per minute.
Describe the relationship shown by these results between the distance of the light source and the volume of oxygen gas collected. Include data from the table to support your answer.
Use the data to estimate the volume of oxygen gas that would be collected in 15 minutes if the light source was placed at a distance of 25 cm25\text{ cm}25 cm. Justify your answer.
44 exam-style questions on OCR GCSE Biology Practical skills. Each one has a worked solution and a mark scheme showing where the marks go.